Topic: Why is my tail light pulsating?

[Canada]

It's been going on a while and does not bother me since I cannot see it but the cops mentioned it to me the other days after pulling me over for "speeding". I think he just wanted to check my bike out but that's always up for debate.

I put a truck led light light in when building up by seat and re-did and cleaned up all of the wiring back in that area. I don't think it would be linked at all but I did but the LED turn signal blinker doodad in since I am running LED front blinkers as well. As I am driving along the light will go from bright to dim and bright.... and I am not so sure it has anything do do with the RPM I am running at that moment.

Is this as simple as the voltage regulator or battery? I don't get the impression that my headlight is doing the same but I could be wrong. I have not really tried to diagnose this on my own but I would appreciate anyone's opinion on this matter.

Cheers!

[IainC]

My guess would be as you rev the bike the voltage jumps a little causing the light to get brighter. I'd suggest giving it a bit of throttle in neutral and seeing if this causes it to get brighter. Maybe someone else has more ideas. 

[Canada]

It's weird, just checked it and it seems fine and does not change at all when I rev. I wonder if it only shows up in the dark. I'll check tonight and see if that is the case.

[Canada]

OK, so it does flicker a bit at idle but nothing that noticeable. If you rev it it brightens up a bit and then flickers quickly. Let off and it tines down again. Anyone have a clue? I'll do a full electrical test sooner then later but does anyone have a sense of what might be doing this?

Thanks

[TwoTired]

The Vreg cycles the alternator power strength to keep the battery voltage in an acceptable range.  If it gets too high the alternatore backs off.  If there is more load than the alternator is currently making then the battery voltage goes down a little and the vreg responds by jacking up the alternator power output.  These changes make the voltage level go up and down  by some amount.  Incandescent bulbs react slower to voltage changes than LEDs.
I'd guess your pulsing is from Vreg cycling.
Depending on the response time of the multimeter, and the frequency of the pulsing, you might be able to see the voltage change on the meter display.

You might also see what the voltage variance is on the tail light power leads, by putting the meter into an AC volts range.  This would then measure the ripple riding on the DC voltage.

You might also check the electrolyte level of the battery.  If it is low, the battery has less ability to smooth out voltage due to load variations and alternator cycling.   Finally, if you have a smaller battery than stock, the reduced impedance can also add to line voltage variations, like a standard battery with low electrolyte.

At any rate, the investigation begins with voltage level monitoring.